They can. But usually it is tougher to do. If you get two females, they may constantly be agressive towards each other. And if you get two males, I dont know if the other female will be enough to prevent on of the new ones from bevcoming female. In a tank your size (75 ga, right?) I'd stick with one species.
I have seen pairs that were mis-matched, like a perc female/oscellaris male, or a gold maroon female/white maroon male.